Lawrence Street Rocket Mass Heater

[cye]

I was delighted to learn that Lawrence Steet Workshops were in the process of building their Rocket Mass Heater to heat the workshops.

I dropped in yesterday and was amazed to see a functioning RMH. Martin fired the thing up with a few small sticks to show me it working. It's not 100% complete yet, but it certainly appears to be functioning very well.

Here's some pics of the fantastic work Martin has done so far. Apologies from me for the poor pics, hopefully you'll see enough to get the idea.

To the left of the pic you can see a square arrangement of fire brick, this is the first part of the J tube, into which the stick fuel is fed. You'll see another more detailed pic of this later


The big red thing is the equivalent of the 'oil drum' more commonly used in RMH. Instead Martin has used the shell of an enormous commercial expansion vessel, much heavier guage than an oil drum. Inside of this there is a vertical flue known as the 'riser'. The riser has a 8" cross section vertical flue insulated with vermiculite. The flue gases rocket upwards inside this long insulated vertical flue and reach very high temperatures, before hitting the inside of the top of the outer 'drum' (the big red tank), and are forced downwards before exiting the red drum into the horizontal flue inside the thermal bench.

The flue then exits the bench to the far right of the pic and rises up the wall above head height, whereupon it exits the wall and vents cleanly to the outside.

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[cye]

This view of the RMH shows the tail end of the RMH 'bench' of the right and the burner end on the left.

The 'bench' is a thermal battery. It contains an 8" horizontal SS flue pipe set into a case of concrete blocks etc and ontop on which flag stones have been placed, ontop of which folks can sit and warm themselves.

Martin has setinsulating blocks between the bench and the wall of the building , possibly thermalite or similar, then the visible side you can see are ordinary concrete blocks. Martin is thinking about pouring in loose sand around the flue to fill in the gaps and to provide additional thermal mass.

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[cye]

This shows the tail end of the thermal bench, where the flue exits the bench and rises up the wall of the workshop before exiting through the wall.

Martin has built into the flue a small metal cube with an access door at ground level where the flue exits the bench. In this pic the hinged access door is held closed with the help of a concrete block. This is provides for occasional ash clean-out but its primary function is to allow 'priming' of the heater. When firing up the heater from cold, in addition to lighting the fire in the J tunnel at the start of the burner, Martin burns some newspaper in the metal cube to warm or 'prime' the tail end of the, thereby providing some initial additional suction for the main fire until the whole burner and heater gets up to working temperature. As the burner will be smokey when it is being lit, this clever addition prevents smoke rising from the feeder end of the J tube.

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[cye]

This shows the very first part of the burner, the opening (fuel feeder) end of the burn tunnel. Long sticks of wood are set vertically into this feed tube and they 'cigar burn' at the bottom only. I.e., flames do not rise and do not work their way upwards to consume the fuel in one go. As the fuel cigar burns from the base, the fuel automatically feeds itself downwards gradually as the base of the wood burns away.

In this pic you can see the flames from the cigar burn shooting sideways from left to right. The flames pass horizontally along the inside of the horizontal base of the J in the firebrick burn tunnel, before being accelerated or 'rocketed' vertically in the metre tall riser.

Perfect for burning longish pieces of scrap wood such as pallet wood.

Read more: www.solarco-op.proboards.com/index.cgi?action=display&board=woodheat&thread=290&page=1#ixzz2ktRU4Qar

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[cye]

This is the outside vent of the flue, after the heater has been running about a quarter of an hour. The burnr has now warmed up, yet there is no visible smoke or smell from the exit. When I hold my hand over the exit, whilst I can feel some warmth, it will not burn me. thus is because most of the thermal energy from the efficient burn has either been radiated from the big red drum, or been captured in the thermal battery of the bench.

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[caveman]

That is brilliant or 'massive' as they say down here. Looking at it makes me just want to sit down and make a brew of tea. We should send a link to Ianto Evans in thanks for his book.

[cye]

Yes, it is a brilliant thing, and for here it is pioneering. I doubt if there is another RMH in the North, and I'm sure this is only one of a very few in Ireland.

Martin is proposing to add a copper water heating coil inside the outer barrel/drum in order to heat water for some radiators. See attached schematic - I've drawn in yellow an approximation of what I think is being considered. It would be something like a 3/4" copper coil.

Any views and comments would be really helpful...

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[caveman]

I am thinking I would put the coil around the lower half of the outside of the oil drum. That way there would be no risk of causing a constriction between the riser and the drum and the coil would not be cooling the riser. Some insulation around it would finish the job. I would use minimum 3/4" pipe.

I am sure someone has thought of this before now but what about air ducts through the storage mass. If they were set in low beside the flue they wouldn't affect the heat of the bench as much as the time it will stay warm for, which would be a decent compromise.
c

[cye]

I passed on your suggestion to Martin when I was speaking to him earlier today. I suggested he hold off doing anything with water heating until we get a hold of ernie wisner's dvd on water heating with a RMH.

Some further info on the LSW RMH:

Both the J-tube and the riser are made from fire brick. this is slightly unusual as most risers are a metal pipe surrounded by insulation, and will heat up fairly quickly, whereas the LSW riser is firebrick surrounded by a 23" diameter metal pipe, with the gap between the two filled with vermiculite and capped with clay. the outer drum is 32" diameter, so there is a gap of 4.5" between the outer drum and the outside of the riser stack.

[caveman]

All that fire brick will take a good while to heat up and might make for a dirty and prolonged start.

[cye]

Yes, I can see why it may take a while longer to heat up than the conventional riser. Those firebricks have a thermal mass to heat up.

Having said that, when I saw it on Saturday fired up from cold, it was not long afterwards that I went outside and discovered there was no obvious smoke or smell, so perhaps it's just 'a short while' compared with the 'very short while' a traditional riser would take!

Anyway, here's a nice pic of the concept, thanks to Richsoil.com

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